Scientists from diverse disciplines met in November 2014 at the Lunar and Planetary Institute (LPI) in Houston to discuss the state of knowledge of volatiles in the interior of Mars. Participants focused on studies of meteorites, observations from remote sensing, laboratory experimental investigations, in situ surface investigations, astrobiological implications, and geophysical and geochemical modeling.

Which observations, instruments, or experiments are needed to make progress on understanding the origin, roles, and evolution of volatiles in the interior of Mars?The goals of the workshop were to examine the latest developments in the field; where data are lacking; and which observations, instruments, or experiments are needed to make progress on understanding the origin, roles, and evolution of volatiles in the interior of Mars. Ultimately, participants sought to synthesize knowledge from diverse scientific fields and focus the primary scientific questions that still need to be addressed.

The workshop sessions, organized by volatile components, focused on the current and ancient atmosphere, chlorine in the interior and interactions with a crustal reservoir, the amount of water in the interior and the effect of water on mantle melting, degassing of magmatic sulfur to the atmosphere, and carbon and the potential for habitability. The main approach used to understand the volatile content of Martian magmas, and thereby the interior, has been the study of Martian meteorites; the investigations discussed at the meeting focused on analyses of hydrous minerals (apatite and amphibole) in the meteorites and their bulk elemental and isotopic chemistry. Some presentations focused on cosmochemical constraints to understanding the Martian interior. Additional talks focused on laboratory experimental simulations, geophysical modeling, and remote sensing (orbiter and rover analyses) to understand the volatile content of the Martian interior and the roles volatiles played in the evolution of Mars.

Chlorine concentration map of the Martian surface. Landing sites for Viking 1 (V1), Viking 2 (V2), and Pathfinder (PF) are labeled, along with Gusev Crater (G) and Meridiani Planum (M). Credit: Keller et al. [2006] via ‪Mars Odyssey GRSWorkshop participants discussed three general processes that have determined the history and present state of volatiles in the Martian interior: accretion of volatile-bearing planetary material from the planetary nebula; catastrophic outgassing due to magma ocean solidification; and degassing by secondary volcanism, with trapping and release of volatiles by crustal processes potentially overprinting the primary information. Discussion focused on the differences among subclasses of Martian meteorites, between Martian meteorites and the chemistry and mineralogy of the surface, and between Mars and Earth.

Questions that arose from the meeting include the following: What is the concentration and heterogeneity of volatiles in the Martian mantle?Some of the questions that arose from the meeting include the following: What is the concentration and heterogeneity of volatiles in the Martian mantle? How has degassing of the mantle through magma ocean crystallization and secondary basalt genesis depleted the volatile content of the mantle and contributed to an early greenhouse atmosphere? How has interaction with crustal and atmospheric fluids overprinted the volatile element and isotopic composition of the Martian meteorites? Participants agreed that to fully characterize the concentration and, importantly, heterogeneity of the volatile content of the Martian interior, it is vital to increase the diversity of the sample collection (in composition, age, petrologic classification, etc.) with meteorites, surface and orbital missions, and, eventually, sample return.

The workshop featured strong international participation, especially from Europe. LPI, the Universities Space Research Association, and NASA’s Mars Exploration Program provided financial support. The Mars Exploration Program contributed travel grants to two graduate students.

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